Aqueous flexographic and gravure inks are widely used in the industry for a number of printing purposes, including printing on plastic packaging films. Resins used as vehicles for water-based flexographic and gravure ink formulations must exhibit certain properties such as solubility in water, wet adhesion to polypropylene film, hydrolytic stability, high melting points, and good pigment wetting.
Alcohol-soluble polyamide resins have been used extensively in inks for packaging and are commercially available. These polyamides are made from dimerized fatty acids and various polyamines such as ethylene diamine or hexamethylene diamine.
The use of such polyamide resins in ink compositions is described in Floyd, D. E., Polyamide Resins, Reinhold Publishing Co., New York, 1958 and in the Encyclopedia of Polymer Science and Technology, Interscience Publishers, John Wiley Sons, Volume 10, New York, 1969. A typical commercial product is GAX-340 manufactured by Henkel.
For water-based ink, a water-soluble resin such as acrylic resin or a conventional soluble maleic resin may be used. Acrylic resins have good film properties, but lack adhesion to polyolefin films.
Conventional soluble maleic resins, which contain half-esters, are subject to a certain degree of hydrolytic instability under alkaline conditions. They also lack film toughness.
Water-based ink compositions are taught in U.S. Pat. No. 4,963,188 to be prepared by free radical polymerization of rosin and maleic anhydride. Modification of the polymer with an alcohol or an amine prior to utilization in preparing the ink composition is disclosed.
Recently, water-soluble resins having qualities of adhesion and wettability for use in packaging ink compositions were developed as the reaction products of rosin modified by Diels-Alder reaction with an .alpha.,.beta. unsaturated acid and a compound containing two secondary amine groups, including commercially available piperazine and N,N'-dimethylethylene diamine. These resins are described in U.S. Pat. No. 5,066,331.
These resins were developed primarily for use in water/isopropanol-based inks for printing on film, where they perform quite satisfactorily. When using these resins in all-water systems (i.e., no alcohol), it was found that the resin solutions had relatively limited shelf stability. In many cases the solutions gel upon standing for two or three days.
U.S. Pat. No. 5,152,832 corrected this gelling problem by teaching the use of a resin derived from the reaction products obtained by reacting a modified rosin with a compound containing two secondary amine groups, and further modifying said reaction products with a polyol (such as diethylene glycol).
However, a major problem exists with the employment of these resins. That is, these resins were found to be totally unsuitable for use as support resins for making acrylic latexes-forming excessive grit whenever these resins were utilized in this manner.
The present invention avoids this problem by teaching the use of a resin derived from the reaction products obtained by reacting a modified rosin with a hydroxyl-containing carboxypyrrolidinone derivative. Suitable hydroxyl-containing carboxypyrrolidinone derivatives are obtained by reacting itaconic acid with an amine and a polyol.
U.S. Pat. No. 5,152,832 (which is hereby incorporated by reference) teaches the production of carboxypyrrolidinones, which are subsequently reacted with alkenylsuccinic anhydrides to produce polyester lubricant additives. This patent does not teach or suggest the reaction of carboxypyrrolidinones with rosin or rosin derivatives.
Therefore, it is an object of this invention to provide water-soluble resins having for use in making acrylic latex compositions. These acrylic latex compositions may be utilized in formulating water-based flexographic gravure ink formulations.